Currently, subsea wellhead stacks are typically installed by using a drilling rig and a string of drillpipe for deployment. A separate umbilical from the rig to the wellhead equipment provides pressurized fluids for testing and commissioning, in addition to electric power and control lines. Typically one or more ROV's are also used in the operation. The time and equipment used is very expensive. In shallow waters, if the drilling rig is on the field and has commenced drilling and then is used to install a few production XT (Christmas trees) and other related equipment, this can be sensible, particularly if the drilling rig still is under contract. However, in deep water, which can be thousands of meters of depth, and with a large number of wellheads, the cost can be tremendous. Sometimes the rig must return for further testing or installation, which adds to the costs. The operation of joining drill pipes to lengths of up to several thousand meters, and large drums with umbilicals, installations for hydraulic power units, hydraulic liquid storage and gas for testing, are all expensive and time consuming. The heavy weight and size require large space, and may require several containers on deck on the rig. Therefore, a demand exists for technology useful for installation and testing of subsea wellhead stacks without using a drilling rig, and technology that make significant cuts in the required equipment and the period of time for such operation.